In the case where the polarity of a power source connected to a load is in a state (hereinafter referred to as “reverse connection state”) that is opposite to a normal state, a reverse connection protection transistor may be used to protect the load. In the case of the reverse connection state, the reverse connection protection transistor serves to prevent flow of current in a direction opposite to that in the normal state.
In the case where the reverse connection protection transistor does not work normally in the reverse connection state, current in a direction opposite to that in the normal state flows in the load. Therefore, in the case where the reverse connection protection transistor does not work normally in the reverse connection state, an undesirable situation, such as a failure in the load, may occur.
Under such circumstances, a technology for diagnosing a failure in a reverse connection protection transistor has been developed. An example of the technology for diagnosing a failure in a reverse connection protection transistor is the technology described in Patent Literature 1.